This invention relates to a charging control apparatus for use in a vehicle wherein a control unit for controlling the state of electric generation by a generator has a decreased number of terminals for external connection.
Charging control systems for vehicles presently in use in this field are classified into a system type I shown in FIG. 2 and a system type II shown in FIG. 4. The system type I shown in FIG. 2 is intended to decrease its size and cost, while the system type II shown in FIG. 4 is intended to accurately control the voltage of a battery mounted on a vehicle.
More precisely, in the system type I shown in FIG. 2, a charging control unit 2, which controls a quantity of power generated by a generator 1 to charge a battery 3 mounted on a vehicle, has a terminal T.sub.1 directly connected to the battery 3 for detecting the condition of the battery voltage. The charging control unit 2 is designed to control the battery voltage at the level of a first preset voltage of 14.5 V which is a normal control voltage level of a battery for a vehicle. Thus, when the level of the voltage detected at the terminal T.sub.1 is equal to or higher than 14.5 V, the control unit 2 operates to decrease a quantity of power generated by the generator 1, while when the level of the voltage detected at the terminal T.sub.1 is lower than 14.5 V, the control unit 2 operates to increase a quantity of electric power generated by the generator 1, so that the battery voltage can be maintained at the predetermined level of 14.5 V.
In the system type II shown in FIG. 4, output signals from various sensors, for example, a battery-electrolyte specific gravity sensor, a battery-electrolyte temperature sensor, a load sensor, etc. are applied to an external control unit (ECU) 6. After the ECU 6 has calculated a desired battery voltage level on the basis of the information output signals from the sensors, the ECU 6 applies an output signal through a terminal T.sub.2 to a charging control unit 2, so that the voltage of a battery 3 can be controlled at the desired voltage level calculated by the ECU 6. However, in the case of the system type II, a source voltage of the ECU 6 itself is supplied by the battery 3. Therefore, the voltage of the terminal T.sub.2, which functions to supply a voltage signal representing the condition of the battery voltage to the charging control unit 2, can not be set to the first preset voltage of 14.5 V, and it is inevitable that the voltage of the terminal T.sub.2 is set to a second preset voltage equal to or lower than a minimum voltage of the battery 3 (for example, approximately 10 V).
However, if it is intended to use only one charging control unit 2 in common with both the system type I and system type II, it becomes necessary for the charging control unit 2 to have at least two input terminals T.sub.1 and T.sub.2 for receiving the voltage signal representing the condition of the battery voltage. That is, in a case where the charging control unit 2 is applied to the system type I, it is necessary to apply the battery voltage to one of the input terminals T.sub.1 of the charging control unit 2 thereby to detect the battery voltage applied to the input terminal T.sub.1. Thus, this input terminal T.sub.1 is necessary for determining whether the detected battery voltage is equal to or higher than the first preset voltage of 14.5 V.
On the other hand, in a case where the same charging control unit 2 is applied to the system type II, because an output signal of several volts from the ECU 6 is used as an input signal to the charging control unit 2, the other input terminal T.sub.2 of the charging control unit 2 is necessary for receiving the input signal and determining whether the input signal voltage is equal to or higher than the second preset voltage of several volts.
Thus, at least two input terminals T.sub.1 and T.sub.2 have been necessary for a single charging control unit 2 used in common with both the system type I and system type II, as described above.
Further, if the single charging control unit used in common with both the system type I and system type II has only one input terminal T, it becomes necessary to raise the voltage level of the output signal of the ECU 6 used in the system type II up to 14.5 V and hence to have a DC-DC converter for boosting purpose provided in the ECU 6, resulting in an undesirable increase in the size and cost of the ECU 6.
Further, if the single charging control unit 2 has a function of detecting disconnection of connection wires from both the input terminals T.sub.1 and T.sub.2 thereof, when the single charging control unit 2 is applied to either one of the system type I and system type II, there was an inconvenience such that an alarm signal indicating the disconnection of a connection wire from the input terminal to be used when the single charging control unit 2 is applied to the other one of the system type I and system type II.